A variety of techniques have been used for separating suspensions of finely divided solids in a liquid solution including filtration, centrifugation, extraction and sedimentation. The details of these techniques are generally well known to those skilled in the art.
Gravitational separation utilizes the force of gravity to promote sedimentation and agglomeration of the heavier components from the mixture and the lighter components in the mixture tend to rise to the surface. The lighter phase is then removed from the surface by skimmers and other well-known techniques.
In order to enhance gravitational separation and coalescence in the prior art, high surface area sieves and plates are placed in the flow of the fluid being separated. Generally, the plates are welded or permanently attached to the sides of the separator tank. Generally, two interceptor plate orientations may be found in phase separators. The first, called the countercurrent design, includes a plurality, of parallel plates which are sloped at an angle either upwardly or downwardly, in the direction of waste water flow. The plates, therefore, force the mixture of liquid containing particles to flow in the direction of the plates' slope, either upwardly or downwardly. For example, when the plates are sloped upwardly, solids impinge on the top surface of the settling plates and slide down the plate due to the force of gravity against the flow of the waste water. When a second set of plates is used in series with the first, for example sloping downwardly, the coalesced lighter phase impinges upon the bottom surface of the plates and is forced to flow along the surface of those plates upwardly, against the flow of the liquid. Accordingly, the term "countercurrent separation" has been used to describe the process carried out in such a system. The disadvantage of the countercurrent separators is that the separated matter, either the lighter phase oil or the heavier phase solids, are always traveling against the flow of the liquid containing solids so that their progress is slowed. In addition, there is a higher tendency for turbulence and mixture of the phase flowing in the countercurrent direction. Another problem in countercurrent separators is clogging of the plates.
A more efficient separator design is embodied in the cross-flow or co-current separators. These separators have their plates sloped normal to the direction of the flow. When several stacks of plates are used, the stacks are arranged in parallel rather than in series. The liquid containing particulates enters the stack of sloped interceptor plates and flows in a parallel fashion through the plates, never forced upwardly or downwardly, since the plates slope downwardly or upwardly in a direction perpendicular to the flow. Therefore, while the liquid containing particulates being separated flows in a parallel fashion, the lighter or liquid phase material rises to the bottom surface of the upper interceptor plates and tends to rise upwardly in the direction of the slope of the plates while still flowing in the same direction of the flow. Likewise, the heavier phase material or solids settle to the top surface of the lower interceptor plates and follows the slope of the plate to the lower side or opposite side of the lighter phase material. Accordingly, both the heavy and lighter phase materials flow in the direction of the current of the liquid being separated, but in an opposite direction from each other across the surface of the plates. This type of separation process is therefore called crossflow co-current separation. The co-current separators have the advantage of reduced turbulence and mixing of the lighter and heavier phase components, since both components travel in generally the same direction of the liquid being treated.
U.S. Pat. No. 5,173,195 (Wright et al) discloses a phase separator apparatus which utilizes phase separator modules for insertion in a separation tank.
U.S. Pat. No. 5,340,470 (Hedrick et al) discloses a phase separator apparatus having multiple stacks of interceptor plates which divide the separation vessel to provide an annular space between the parallel interceptor plates and the vertical wall of the separation vessel to thereby form an inlet manifold for the plates which manifold provides a uniform, uninterrupted flow to each stack of plates. The arrangement of plates also forms an outlet manifold which provides a uniform flow from each stack of plates and directs the liquid stream having a reduced level of finely divided suspended particles downward in the separation vessel to an exit in the lower end of the vessel. The feed liquid is introduced into the lower end of the separation vessel with an inlet distributor which initially directs at least a majority of the feed liquid in a generally downward direction to effect a primary separation prior to being introduced into the stacks of parallel interceptor plates. The introduction of the feed liquid and the exit of the separated product streams from the lower end of the separation vessel balance the velocity heads on either side of the stacks of the parallel interceptor plates and eliminates horizontal surfaces which would accumulate solids.
Many of the prior art apparatus have complicated internal components which are expensive to construct and not suitable for certain heavy, viscous feedstocks because of potential plugging problems. In addition, an apparatus with a high density of relatively fragile internals is susceptible to unexpected pressure surges which can cause structural damage to the internals.
Accordingly, what is needed is a phase separator apparatus which is able to perform the desired separation while minimizing the complexity of the internal components. Those skilled in the prior art have sought a separation apparatus capable of high performance with the advantage of more open internal volume to provide the concomitant lower velocity for a given cross-sectional area.